The owner of mobile operator Three is reportedly in talks to buy larger UK rival O2 from Spain's Telefonica.

Last year it was rumoured that BT was interested in buying O2 to return as a fully fledged mobile operator after originally selling O2 to Telefonica, but it instead moved to buy EE, which owns the T-Mobile and Orange brands. Before a name change O2 was BT Cellnet.

Three SingItKitty advert
Three, which ran the successful #SingItKitty advert last year, is in talks to buy O2. Image credit: Three

BT and EE are still talking to finalise a deal worth around £12.5 billion, and now Three-owner Hutchison Whampoa in Hong Kong has reportedly moved to buy O2 for up to £9 billion, furthering the potential shake-up in the UK mobile market.

Three is the smallest UK mobile operator with around 8 million customers, but its owner is known to buy rival networks. Last year, Three acquired the O2 network in Ireland.

As O2 has around 23 million customers, any Three acquisition would make it the biggest mobile operator ahead of EE.

Telefonica has been forced to consider an O2 sale because it is struggling to reduce debts in the face of a stumbling Spanish economy. BT and other major providers want to marry mobile, TV, broadband and traditional voice services to offer a quad play package to win more business, so EE would be the final piece in the jigsaw.